You email a photo from your iPhone, and the person on the other end says it won't open. The culprit is almost always a HEIC file. Here's what HEIC is, why it causes trouble, and the quick fix.
What is a HEIC file?
HEIC (High Efficiency Image Container) is the format iPhones and iPads use to save photos by default. It's based on the HEIF standard and stores a photo at roughly half the size of a JPG at similar quality. Great for saving space on your phone — less great when you need to share it.
Why HEIC won't open elsewhere
HEIC is well supported inside Apple's ecosystem but poorly supported outside it. Many Windows PCs, older Android phones, websites, editing apps and government upload forms simply can't read it. So a photo that looks fine on your iPhone becomes an "unsupported file" everywhere else.
The fix: convert HEIC to JPG or PDF
The simplest solution is to convert HEIC to a universal format. Use HEIC to JPG to turn photos into standard images that open anywhere, or HEIC to PDF to combine photographed documents into one PDF you can upload. Both run in your browser, so your photos are never uploaded.
Stop your iPhone making HEIC files
If you'd rather avoid the problem entirely, change your camera setting: open Settings → Camera → Formats and choose Most Compatible. Your iPhone will then save new photos as JPG. (You'll use a bit more storage, but you'll never hit the "can't open" issue again.) Existing HEIC photos still need converting.